[Messaging sync] Use navigation timestamp for determining unread status

This CL uses the navigation timestamp to determine the read status
of a tab. It fixes a few things
1. Messaging service will clear dirty dots as per seen status
during OnTabAdded and OnTabUpdated methods.
2. An optimization is added to avoid updating the seen timestamp if
it's already ahead of the navigation timestamp thereby reducing
unnecessary commits to sync.
3. Navigation timestamp is updated when a tab is navigated locally
to keep it more accurate.

Bug: 417304360
Change-Id: I98027c9c46e28b5f9e87c520a67001b29a33c5cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6607813
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Mickey Burks <mickeyburks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1468756}